Ferrule assembly

ABSTRACT

A process for preparing terminated fibers comprising: (a) positioning at least one fiber in a ferrule such that a portion of the fiber extends beyond the mating face of the ferrule; (b) affixing the fiber relative to the ferrule; and (c) cleaving the portion of the fiber.

REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.60/377,267, filed May 2, 2002 and hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates generally to an optical component, and,more specifically, to a ferrule-containing optical connector.

BACKGROUND OF INVENTION

Optical fiber connectors are an essential part of substantially alloptical fiber communication systems. For instance, optical connectorsare used to join segments of fiber into longer lengths, to connect fiberto active devices such as radiation sources, detectors and repeaters,and to connect fiber to passive devices such as switches andattenuators. The principal function of an optical fiber connector is tohold a fiber end such that the core of the fiber is axially aligned withthe optical path of the component to which the connector is mated (e.g.,another fiber, a planar waveguide, or an opto-electric device). Thisway, light from the fiber is optically coupled to the other component.

It is well known that to effect optical coupling and minimize Fresnelloss, “physical contact” should be made between the fiber end and theoptical path of the mating device. To effect physical contact,traditionally optical connectors have employed a “ferrule,” which is awell-known component for holding one or more fibers such that the fiberends are presented for optical coupling. Ferrule connectors typicallybias the ferrule forward such that, when the connector is mated to amating component, a mating face of the ferrule urges against the matingcomponent to physically contact the fiber end face with the optical pathof the mating component.

To effect such physical contact, a conventional ferrule typicallyrequires polishing. A polished ferrule may best be described by way ofcontrast to an unpolished ferrule. An unpolished ferrule has a geometryand anomalies on its mating face which make it difficult, if notimpossible, to bring the end face of fiber housed therein into physicalcontact with the optical path of the mating component. In addition, whenmultiple fibers are affixed to an unpolished ferrule, the positions ofthe fiber ends tend to vary along the mating axis, thereby making itdifficult to effect optical coupling with all of the fibers. Polishingthe mating face of the ferrule tends to minimize these variances andshape the mating face of the ferrule to present the fiber ends in aneven plane for mating.

Unfortunately, to minimize the variances and shape the ferrule,polishing must be performed to exacting standards. Polishing thereforetends to be costly and prone to reworking and waste, thereby loweringyields. The problems associated with polishing the ferrule areexasperated in multi-fiber ferrules which are more complicated topolish.

Therefore, there is a need for optically coupling a fiber-containingferrule to an optical path of a mating component without polishing theferrule. The present invention fulfills this need among others.

SUMMARY OF INVENTION

The present invention provides for a ferrule assembly that overcomes theaforementioned problems and offers enhanced configurability.Specifically, the applicants have developed an approach for terminatinga fiber in a ferrule which separates the functions of preparing thefiber's end face for optical coupling and positioning the fiber withinthe ferrule. This is a departure from conventional approaches in whichthe two functions are performed in a single polishing step. By treatingthe functions individually, the fiber end face can be preparedindependent of the ferrule, thereby eliminating the need to polish theferrule/fiber assembly. Generally, it is preferred that the fiber becleaved after it is disposed in the ferrule to minimize handling of thefiber end face which can blemish or otherwise optically degrade the endface. Furthermore, since the ferrule assembly is not subject topolishing, the axial position of the end face relative to the ferrulecan be addressed independently from its preparation. This facilitatesprecise axial positioning of the fiber end face relative to the ferrule.Generally, it is preferred to have the fiber end face protrude from theferrule to enhance its ability to make physical contact for opticalcoupling.

One aspect of invention is a process of preparing a ferrule assemblywithout polishing the ferrule. In a preferred embodiment, the processcomprises: (a) positioning at least one fiber in a ferrule such that aportion of the fiber extends beyond the end face of the ferrule; (b)affixing the fiber relative to the ferrule; and (c) cleaving the portionof the fiber. Preferably, the cleaving is effected by laser cleaving.

Another aspect of the invention is a ferrule assembly made from theprocess described above. In a preferred embodiment, the ferrule assemblycomprises: (a) an unpolished ferrule defining one or more pathways, eachpathway being adapted to receive a fiber, and a mating face; and (b) afiber in each pathway, each fiber having an end face which is suitablefor optical coupling. Preferably, the fiber protrudes from the matingface.

Yet another aspect of the invention is an optical package having aferrule assembly with an unpolished ferrule. In a preferred embodiment,the optical package comprises: (a) a housing; (b) a ferrule assemblydisposed at least partially in the housing, the ferrule assemblycomprising at least (i) an unpolished ferrule defining one or morepathways, each pathway being adapted to receive a fiber, and a matingface; and (ii) a fiber in each pathway, each fiber having an end facewhich is suitable for optical coupling. Preferably, the optical packageis a connector.

Another aspect of the invention is an optical package having a ferruleassembly with an unpolished ferrule in which the fiber end is shaped andthe end face of the ferrule is normal to the fiber. In a preferredembodiment, the optical package comprises: (a) a housing having aregister surface; (b) a ferrule assembly disposed at least partially inthe housing, the ferrule assembly comprising at least (i) an unpolishedferrule defining one or more pathways, each pathway being adapted toreceive a fiber, and a mating face normal to the pathways and abuttingthe register surface of the housing; and (ii) a fiber in each pathway,each fiber having a shaped end face which is suitable for opticalcoupling. Preferably, the optical package is an expanded beam connector.

Still another aspect of the present invention is a system of connectorsand other optical packages which employ ferrule assemblies havingunpolished ferrules which can mate with other ferrule assemblies havingeither polished or unpolished ferrules.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart of a preferred process of the present invention.

FIG. 2 a shows the effect of a converging laser beam on a fiber duringcutting when the beam is held perpendicular to the fiber.

FIG. 2 b shows the effect of the same beam as in FIG. 2 a but at angle αfrom the fiber.

FIGS. 3 a and 3 b show top views of different end face geometries formedthrough laser cleaving.

FIGS. 4 a and 4 b show a preferred approach for laser cleaving when thedistance between the ferrule mating face and the fiber end face issmall.

FIGS. 5 a and 5 b show the mating of a ferrule assembly of the presentinvention with polished ferrules having undercut and protruding fibers,respectively.

FIG. 6 shows an insert of an expanded beam connector in which the endface of the fiber is angled to reduce back reflection.

DETAILED DESCRIPTION

Referring to FIG. 1, a flow chart 100 depicting an overview of apreferred method of the present invention is shown. In step 101, aferrule for an optical connector is provided. The ferrule has one ormore pathways to receive fibers therein. In step 102, one or more fibersare positioned in the pathways of the ferrule such that a portion ofeach fiber extends beyond the end face of the ferrule. At this point, adecision block 103 is reached in which the process of the presentinvention follows a path A or path B. If path A is followed, the processproceeds to step 104 in which the fibers are cleaved. Cleaving thefibers can be performed using any traditional technique, although lasercleaving is preferred. Once cleaved, the process proceeds to step 105,in which the position of the fibers relative to the ferrule is secured,thereby forming the ferrule assembly. As used herein, the term “ferruleassembly” refers to a ferrule having one or more fibers terminated init. At this point, the process proceeds to step 106, in which theferrule assembly is incorporated into an optical package which may be,for example, a connector or other ferrule-containing device. Referringback to decision block 103, if path B is followed, the process proceedsfirst to step 105 (rather than step 104), in which the position of thefibers with respect to the ferrule is secured. Next, in step 104, thefibers are cleaved, thereby completing the ferrule assembly. Again, theprocess concludes with the assembly of the ferrule assembly into theconnector or ferrule-containing device in step 106. Each of these stepsis discussed in greater detail below.

Step 101 involves providing at least one ferrule. The ferrule comprisesone or more pathways, each pathway being adapted to receive a fiber, anda mating face, which, in the final ferrule assembly, presents each fiberend for optical coupling to an optical pathway of a mating component.The pathways may be, for example, bore holes or V-grooves. Such ferrulesare well-known in the art and include for example, MT-style ferrules(such as those used in the MT-RJ and Lightray MPX7 ferrules), SC-styleferrules, and LC- and MU-style ferrules.

Generally, ferrules are made of ceramic or polymeric material. Suchmaterials are suitable if the process of the present invention followspath A, wherein cleaving is performed prior to affixing the fibersrelative to the ferrule. That is, if the fibers are cleaved before theyare affixed to the ferrule, they can be extended well past the matingface of the ferrule such that the cleaving operation does not interferewith the ferrule or vice versa. However, if the process follows path B,and cleaving occurs after the fibers are affixed to the ferrule, it isunlikely that the cleaving process can be isolated from the ferrule tothe extent that there will not be some interference therebetween. Thisinterference may preempt the use of mechanical-type cleaving due to thephysical interference between the mating face of the ferrule and thecleaving mechanism. Thus, in such a situation, laser cleaving may be theonly viable cleaving alternative.

Laser cleaving, however, tends to impart a great deal of heat in thevicinity of the cleave, which in a preferred embodiment may be less thana half a millimeter from the ferrule. At a typical distance of less than0.5 millimeters from the end face of the ferrule, and using a typicalCO₂-type laser, one can expect the temperature at the ferrule end faceto approach that required to ablate optical fiber. Such temperatures areproblematic for conventional polymeric materials such as, e.g. PPS,which is used in MT-type ferrules. Specifically, polymeric materialstend to degrade, melt or deform at such temperatures, therebycompromising the physical integrity of the ferrule and distorting itbeyond typical allowable tolerances. Furthermore, ceramic materialstypically used in ferrules are prone to cracking at such temperatures.

Due to the proximity of the laser to the ferrule end face in path A, itis preferable for the material at the mating face of the ferrule (herein“mating face material”) to either (a) reflect energy, or (b) absorb thelaser energy without damaging the ferrule or the fibers containedtherein. With respect to reflecting the laser energy, suitable materialspreferably reflect at least 90% of the laser light. Since thereflectivity of a material is dependent on the wavelength of the beam,the choice of mating face material will depend on the type of laserused. For example, copper is well suited for a CO₂ laser. With respectto absorbing the laser energy without deformation or degradation,suitable materials have a heat capacity greater than water. Examples ofsuitable materials include, for example, high temperature ceramics whichare well known.

In the embodiment in which a reflective material is used to reflectlaser energy, just the end face may comprise such a material, althoughit may be preferable to form the entire ferrule of such a material froma simplicity standpoint. Likewise, in the embodiment in which anenergy-absorbing material is used, the material may be used just at themating face (providing that an adequate mass of material is present toabsorb and dissipate the heat) or the entire ferrule may be made fromsuch a material.

As mentioned above, a conventional ferrule end face is typicallypolished to remove all anomalies therefrom and to present the fiber endsfor coupling. However, the ferrule of the present invention does notrequire such polishing since the fiber ends are polished during thecleaving step 103. Therefore, in a preferred embodiment, the ferrule isunpolished. As used herein, the term “unpolished ferrule” refers to aferrule has not been polished or is not polished to the extent typicallyrequired to achieve physical contact.

An unpolished ferrule in this context has a number of distinguishingcharacteristics. First, an unpolished ferrule typically has surfaceanomalies on its end face which tend to interfere with the matingsurface of the mating connector or device and prevent end faces offibers from making physical contact with mating optical pathways. Forexample, ridges or bumps on the mating face of an unpolished ferruleprevent the mating face from making good physical contact with aperfectly planar surface. Those skilled in the art will understand thatthese surface anomalies tend to make physical contact in the center ofthe mating face most difficult, which is particularly problematic sincethe center of the ferrule is typically where the fibers are located.Obviously, as the mating face of the ferrule becomes larger in area, aswith MT ferrules, the probability of surface variations andimperfections increases along with the number of fibers requiringphysical contact. Polishing the ferrule removes these surface anomalies.Generally, for an MT connector, the surface irregularities are removedduring polishing such that the maximum gap between the mating face ofthe ferrule and a perfectly flat plane is less than about 0.25 μm Bycontrast, an unpolished ferrule may have a gap between its mating faceand a perfectly flat plane of greater than about 2.5 μm Another approachfor mitigating the effects of surface anomalies on the mating face is topolish a dome on the mating face such that the fibers are located at theapex of the dome. This guarantees that the end faces of the fibers areon the leading surface on the mating face along the mating axis, and,thus, any anomalies toward the edges of the ferrule will not prevent thefibers from contacting the mating surface. Obviously, an unpolishedferrule has no dome.

Polishing the ferrule is also required to cause the fiber end faces toprotrude a certain distance from the ferrule's mating face. This is dueto the fact that MT ferrules typically comprise a polymer material whichtends to abrade more quickly than the fibers during polishing. As theferrule material abrades around the fibers, the fibers effectivelyprotrude from the mating face. Such a protrusion increases thelikelihood of the fiber end faces making physical contact with themating optical pathway of a mating structure. According to U.S. Pat. No.5,743,785, in a polished ferrule, the ends of the fiber should protrudefrom the ferrule's mating face by about 0.5 to about 2.5 μm, or, inother terms, from about 0.4 to about 2% of the fiber's diameter.Therefore, with an unpolished ferrule, the fiber protrudes by less than0.5 μm or by greater than 2.5 μm from the ferrule's mating face, or byless than 0.4% or by greater than 2% of the fiber's diameter.

Therefore, as used herein, the term “unpolished ferrule” refers to aferrule having one or more of the following features: (1) a gap ofgreater than about 2.5 μm between the mating face of the ferrule and aperfectly planar surface, (2) a mating face which is not domed, and (3)a fiber protrusion of less than 0.5 μm or greater than 2.5 μm from theferrule's mating face, or less than 0.4% or greater than 2% of thefiber's diameter. In samples of 100 or more connectors of the presentinvention, at least 90% have one or more of these characteristics and atleast 70% have two or more of these features.

Step 102 involves disposing a fiber in each pathway of the ferrule suchthat a portion of the fiber extends beyond the end face of the ferrule.Each fiber is positioned such that a sufficient portion extends beyondthe end face of the ferrule to facilitate cleaving thereof. The extentto which a fiber extends from the ferrule will depend upon the cleavingtechniques used. For example, a mechanical type cleaving methodtypically required more space than a laser cleaving approach and thusthe fiber needs to extend further beyond the ferrule mating face toaccommodate the mechanism One skilled in the art will readily understandto what extent the fibers should be extended past the mating face of theferrule to facilitate cleaving thereof.

Step 104 involves cleaving the fiber. The fiber is cleaved to produce anend face which is suitable for optical coupling. As used herein, an endface that is suitable for optical coupling is one in which has nooptical or mechanical defects (e.g. no change in refractive index, noscratches or chips, etc.).

Cleaving the fibers may be performed either mechanically or by lasercleaving. With respect to mechanical cleaving, this is a well-knowntechnique and involves essentially shearing the fibers cleanly toprovide a mating face. It may be preferred to polish a mechanicallycleaved end face of the fiber. Methods of performing this polishing arewell-known and may include, for example, physical grinding/polishing and“laser polishing” in which a laser is used to melt and thereby smooththe end face of the fiber. Although mechanical cleaving is certainlycontemplated in the present invention, the preferred method of cleavingis laser cleaving.

A preferred process for laser cleaving is described in U.S. Pat. No.6,246,026, incorporated herein by reference, and pending U.S.application Ser. No. 09/880,698, also incorporated herein by reference.

In the laser cleaving process, optical fiber material is ablated ratherthan melted. This requires the laser to impart sufficient energy intothe fiber to effect its immediate sublimation In general, any laser witha wavelength between 0.1 and 1.5 μm and 8.5 μm to 10 μm can be used forproducing the beam for cleaving the fibers. Suitable lasers include, forexample, CO₂ and excimer lasers, although a CO₂ laser is preferred. CO₂lasers have proven particularly advantageous due to the high speed atwhich they can be operated and resulting cost effectiveness.

Balancing the objective of delivering high energy to fiber to ablate theglass is the need to minimize the energy absorbed by the glasssurrounding the cut so as to minimize melting adjacent the cut. For thisreason, the laser is preferably operated in a pulse mode for cutting thefiber. In the pulse mode, the laser transmits short high-energy pulsesof laser light so that the material of the fiber is sublimated. Thepulses are very short and have very steep edges, thus, the maximum pulseenergy is achieved very rapidly. For example, suitable results have beenachieved in which the peak power of the pulse is between about 0.1 andabout 1000 watts and the pulse length is greater than about 50 fs. Verygood results are achieved with a CO₂ laser (wavelength 10.6 μ) having apulse length of 35 μs and a peak power of 600 watts.

Although operating the laser in pulse mode is preferred generally,particularly with high power lasers such as a CO₂ laser, someapplication may favor operating the laser in a continuous wave mode. Forexample, if the contact time between the laser and fiber is decreased,i.e., the laser cuts across the fiber more quickly, it may be desirableto operate the laser in continuous wave mode.

Directing the laser beam on the fiber to effect the cut is subject toseveral variables involving the angle of the beam to the fiber and theaxial position of the beam along the fiber. The angle of the beam isdefined by two angles α and θ which are defined with respect to theCartesian coordinate system in which the optical axis of the fiber isalong the z axis and the y and z axes are perpendicular to each otherand the z axis. Angle α corresponds to the angle of the beam from the yaxis, while angle θ corresponds to the angle of the beam from the xaxis. For purposes of illustration, the x axis will be considered thehorizontal axis and the y axis will be considered the vertical axisunless otherwise stated. It should be understood, however, that thisorientation is arbitrary and by no means limits the scope of theinvention

Before addressing the particular angles θ and α, an understanding of thegeometry of the laser beam and its cutting tendencies through fiber isworthwhile. In a preferred configuration, laser cleaving is performedusing a combination of a laser and a convergent lens. This combinationproduces a beam having an angle of convergence of β from the centerlineof the beam. Since the beam is converging and not collimated, its angleof incidence with the fiber is not simply parallel to the beam'scenterline. Rather, the beam's perimeter contacts the fiber at an angleβ relative to its centerline. In other words, the laser beam can bevisualized as a conical beam that contacts the fiber substantially alongthe perimeter of the cone. Furthermore, the beam's effect on the fiberis not limited to just the area defined by the beam. Heat from the beamextends past the beam and ablates fiber material adjacent to it. Thedegree to which the adjacent fiber material is affected is a function ofthe time it is exposed to the beam—the longer the exposure the morematerial is ablated. Therefore, rather than cutting the fiber along thecenterline of the beam, the fiber will be cut along a line which greaterthan angle β from the beam's center line.

For example, referring to FIG. 2 a, a schematic is shown of a beam 201having an angle β of convergence and an angle α of zero. Rather thancutting an end face essentially normal to the optical axis 202 of thefiber 200, such a configuration results in an end face 203 having aparabolic profile, which is generally undesirable. More specifically, asthe laser cuts from top to bottom, the top 204 of the fiber is subjectedto the beam for a longer time than the bottom 205. Additionally, sincethe beam is converging the beam at the top of the fiber will be widerthan at the bottom of the fiber. The combination of longer exposure timeand a wider beam results in the aforementioned parabolic profile.

To avoid a parabolic profile, the laser must be directed at the fiber atan angle a as shown in FIG. 2 a. The angle α depends upon the angle ofconvergence and the cutting time/energy level of the beam For example,to prepare an essentially normal end face 206, angle α should be about30° for a CO₂ laser having a peak energy level of about 600 watts.

The angle θ is variable and depends upon the desired end face geometry.For example, if a planar end face which is essentially normal to theoptical axis of the fiber is desired, then angle θ will be about 0.Often it is preferred to bevel the end face of the fiber, particularlyin single mode applications in which it is desirable to minimize backreflection To this end, a common angle θ for single mode fiber end facesis about 8° as shown in FIG. 3 a which is a schematic top view of afiber 301. Aside from planar or nearly planar end faces, the lasercleaving approach of the present invention can provide for multifacetedor curved end faces. For example, in a preferred embodiment, lasercleaving can be used to form a wedged-shaped fiber end as shown in FIG.3 b which is a schematic top view of a fiber 302. Such a configurationis well suited for optically coupling the fiber with pump-type lasers orother devices which emit or receive an elliptical beam of light.

Generally, it is preferred that the beam impinge on the portion of thefiber that extends a distance d_(o) from the mating face of the ferrule.As used herein, the term “distance d_(o)” refers to the shortestdistance between the mating face of the ferrule and the end face of thefiber formed after cleaving. It should be understood that distanced_(o)is not defined by the distance between the mating face of theferrule and the centerline of the beam since the beam does not cut alongits centerline as discussed above. The distance d_(o) can vary dependingupon the cleaving technique. The distance d_(o) is not as critical withpath B, since the fiber's axial position with respect to the mating faceof the ferrule can be adjusted after cutting. On the other hand, withpath A, in which the fibers are fixed and then cleaved, the distanced_(o) is critical since it is the distance between the end face of thefiber and the mating face in the final fiber assembly (herein “distanced_(f)”). There is no opportunity in path A to readjust the fiber'sposition with respect to the ferrule's end face after it has been cut.

It has been found that for a particularly small distance d_(o) themating face of the ferrule will interfere with the laser beam. Thisinterference can result in a distortion of the laser beam which canaffect the accuracy of the laser cut. Additionally, this interferencemay result in a greater than desired absorption of energy by the ferrulewhich may cause it to distort or degrade. Accordingly, in the case ofsmall distance d_(o), it may be preferred to use a cleavingconfiguration as shown in FIGS. 4 a and 4 b to avoid this interference.As shown in FIG. 4 a, a ferrule 401 has a domed or beveled mating face401 which is angled away from the fiber 404 at an angle φ. The beam 402has a convergence angle β. It is well known that a converging beam willmeet and then diverge. In this configuration, the beam is positionedsuch that cleaving is performed at about the point of convergence or atthe waist 403 of the beam If φ is equal to or greater than β and thebeam is substantially perpendicular to the fiber, then the beam shouldavoid the mating face of the ferrule. If the beam is not substantiallyperpendicular to the fiber, but instead at angle α to the fiber (as ispreferred), then the angle φ needs to be equal to or greater than α+β.

The way in which the fibers and laser beam are moved relative to eachother to effect the cuts described above can vary and it is anticipatedthat any approach which is precise, accurate and repeatable willsuffice. In a preferred embodiment, a device is used which maintainsangle α between the beam and the fiber and moves the fiber at one ormore predetermined angles θ relative to the laser beam. It is within thescope of the present invention, however, to move the laser beam relativeto the fiber.

The laser cleaving process has a number of advantages over traditionalmechanical cleaving approaches. Perhaps the most significant advantageis that laser cleaving produces a very smooth fiber end face soadditional machining of the fiber end after cutting—as is normal withmechanical cutting processes—is no longer necessary. Elimination ofpolishing is very significant. Not only is polishing a difficult andtime-consuming task, which is prone to error (and therefore waste), butit also affects the axial position of the fiber end face. That is,polishing grinds or otherwise alters the physical features of the endface and thereby affects the axial position of the fiber end. Thiseffect can be critical in the case of a multi-fiber array (e.g., ribboncable) in which variation in axial position of the various fibers cannotbe tolerated. More specifically, if the end faces are at different axialpositions, they are prevented from simultaneously making physicalcontact with optical paths of the mating component. According to U.S.Pat. No. 5,743,785, for an MT ferrule, the end face variation or “delta”among the fibers along the mating axis should be not greater than about0.4 □m and preferably not greater than about 0.2 μm. Axial positioningof the end faces is also critical if path B is chosen and the fiber issecured relative to the ferrule before cutting. Because a laser-cleavedfiber does not need to be polished, the axial position of its end faceis not subject to this variation. Laser cleaving typically cleaves theend face with an axial position accuracy of 0.1 μm. Therefore, in anunpolished MT ferrule, the end face delta will typically be no greaterthan about 0.4 μm, and preferably no greater than about 0.2 μm.

In step 105, the fibers are affixed such that their relative positionwith respect to the ferrule is fixed. Methods of fixing the fiberspositioned relative to the ferrules are well-known and include, forexample, applying epoxy to the ferrule pathways. Other techniques forfixing the fibers position may include, for example, clamping the fiberin an object which is in fixed relation to the ferrule (see, forexample, U.S. Pat. No. 6,200,040 which discloses such a claimingmechanism, i.e., the slice element).

In path A, where the fiber's position is fixed relative to the ferruleafter the fibers are cut, the fiber is moved such that its end face isdistance d_(f) from the mating face of the ferrule. Thus, in thesituation where the fiber is cleaved a distance d_(o) from the matingface of the ferrule, in step 104, that distance is decreased to d_(f).

In one embodiment, the mating face of the ferrule is pushed flushagainst the flat surface so that the distance d_(f) is equal to 0.Alternatively, it may be preferred to allow the fiber to protrudesomewhat from the mating face of the ferrule such that distance d_(f) isgreater than 0. For example, as discussed in detail below, it isrecognized that a fiber that protrudes from the mating face of theferrule is often more likely to make physical contact with the opticalpath of the mating component. That is, if the fiber protrudes from themating face, then any anomalies on the mating face which might otherwiseprevent the mating face from forming intimate contact with the matingface of the mating component. A protruding fiber does not require suchintimate contact between mating faces. Thus, there is no need to deformthe ferrule as is often necessary in conventional type physical contactconnectors.

Aside from avoiding problems associated with forming intimate contactwith the mating surface of the ferrule and deforming the ferrule, aprotruding fiber also enables physical contact to be made with a matingconnector in which the fiber is undercut from the ferrule. That is, itis not uncommon during the polishing process for the end face of thefiber to recede within the ferrule such that the mating face of theferrule extends beyond the end face of the fiber. Clearly, in such asituation, physical contact with the end face of the fiber is madedifficult. However, a fiber that protrudes from the mating face of theferrule is able to extend into the ferrule of the mating component andmake contact with the end face of the fiber contained therein.

The ferrule assembly of the present invention is uniquely suited tofacilitate fiber protrusion since the fiber end and ferrule mating faceare not polished simultaneously as in the prior art. Polishing a ferruleand fiber assembly together results generally in a fiber end face whichis flush with the ferrule mating face. The approach of the presentinvention polishes the fiber end independent from the ferrule (in fact,preferably, the ferrule is not even polished). Thus, the fiber endposition with respect to the ferrule end face is fully configurable.

Countering the desire for the fiber to protrude from the mating face ofthe ferrule, is the recognition that fibers tend to be delicate andsubject to damage. The possibility for damage or breakage increases asthe fiber length protruding from the mating face of the ferruleincreases. Accordingly, it has been found that preferred distances d_(f)are from about 0 to about 20 μm, and more preferably from about 1 μm toabout 5 μm.

Positioning the fiber a distance d_(f) from the mating face of theferrule can be accomplished in different ways. If distance d_(f) isabout 0, a preferred way to position the fiber is to press the matingface of the ferrule with the fiber protruding therefrom against a flatsurface to thereby push the fiber backward relative to the ferrule untilit is flush with the mating face of the ferrule. More complicatedposition approaches are required if the distance d_(f) is greater than0. Suitable approaches include, for example, pushing the ferrule to aflat under a small angle or use translation stages, or any other way ofmoving the fiber while measuring the fiber end face position.

In step 106, the ferrule assembly having the fibers cleaved and affixedrelative thereto is assembled into an optical package. As used herein,the term “optical package” refers broadly to an assembly comprising afiber-terminated ferrule assembly and may include, for example, aferrule-containing connector (e.g., multi-fiber connectors such as theLightray MPX7 connector, MT-RJ connector, and MTP connector, andsingle-fiber connectors such as the SC-, FC-, LC-, and MU-typeconnectors), or a ferrule-containing device (e.g., passive devices, suchas, add/drop filters, arrayed wave guide gratings (AWGs),splitters/couplers, and attenuators, and active devices, such as,optical amplifiers, transmitters, receivers and transceivers). As iswell known, the ferrule assembly in the optical package holds a fiberend such that the core of the fiber is axially aligned with the opticalpath of the mating component to which the connector or device is mated.This way, light from the fiber is optically coupled to the othercomponent. The term “optical pathway” as used herein refers to anymedium for conducting optical signals, and includes, for example, afiber or waveguide, a silica or polymeric structure in a substrate, or asilica or polymeric optical component. The term “mating component”refers to an optical package that contains or comprises the opticalpathway, and may include, for example, optical connectors and opticaldevices as mentioned above. A mating component typically comprises amating surface which is adapted to receive the mating face of theferrule to optically couple the fiber(s) with the mating opticalpathway(s). Such mating surfaces are well known in the art.

Optical packages comprising the ferrule assembly of the presentinvention have a number of advantages over traditionalferrule-containing packages. First, as mentioned above, the ferruleassembly of the present invention obviates the need for polishing. Thisresults in significant simplification of the assembly process and asignificant reduction in costs. Aside from this advantage, however, thepackage of the present invention also has performance related advantagesover traditional connectors and packages.

Perhaps the most significant performance advantage is derived from theconfigurability of the fiber's protrusion from the ferrule mating face.The protrusion not only allows for the use of an unpolished ferrule butalso facilitates mating with an unpolished ferrule. Thus, the ferruleassembly of the present invention does away with the need for polishedferrules entirely, thereby reducing costs among various opticalpackages. Furthermore, the fiber's protrusion can even be exploited tocompensate for uncut of a polished or unpolished ferrule.

FIGS. 5 a and 5 b are schematic views of the ferrule assembly of thepresent invention optically coupling with a polished ferrule having anuncut and a protrusion, respectively. Referring to FIGS. 5 a and 5 b,the ferrule assembly 501 of the present invention is shown comprising aferrule 502 and a fiber 503 disposed therein which protrudes from themating face 504 of the ferrule 502. In FIG. 5 a, the ferrule assembly501 is shown making physical contact with a polished ferrule assembly505 of a mating component. Like the ferrule assembly of the presentinvention, ferrule assembly 505 has a ferrule 506 and a fiber 507disposed therein. However, unlike the ferrule assembly of the presentinvention, fiber 507 does not protrude from the ferrule, but rather isundercut a distance d_(u) from the mating surface 508 of the ferrule.Although distance d_(u) is best minimized and preferably zero, theferrule assembly of the present invention nevertheless can opticallycouple with mating ferrule assemblies having d_(u) from 0 to about 0.5mm. Referring to FIG. 5 b, the ferrule assembly 501 is shown mating witha ferrule assembly 509 in which a fiber 510 protrudes from the matingsurface 511 of a polished ferrule 512.

In addition to the connector of the present invention being moretolerant of variations in the mating components, it also does notrequire the same degree of mating force as does a traditional connector.It is well known that to effect physical contact of conventionalferrule-containing connectors, the ferrules must be biased forward suchthat when mated the ferrules urge against each other. This force isneeded to deform the ferrules and ensure physical contact between thefibers therein. The force with which a ferrule contacts a mating ferruleis referred to as the mating force which is significant. The matingforce imparted by connectors becomes problematic as the number ofconnectors on a given substrate increases. For example, a card havingmany optical connectors can experience significant force to the extentthat the card deforms or is forced out of its slot by the mating forceof the optical connectors thereon.

The connector of the present invention does not require such high matingforces. Since the fiber preferably protrudes from the ferrule, there isno need to deform the ferrule to effect physical contact between thefiber end face and the mating component. Therefore, the mating force ofthe connector of the present invention is less than that required todeform the ferrule therein. The present invention thus offers advantagesover polished ferrules not only with respect to simplifying thepreparation of a terminated connector, but also with respect toimproving the performance of physical contact ferrule connectors.

Yet another advantage offered by the present invention over conventionalpolished ferrules is the fact that the mating face of the ferrule andthe end face of the fiber are not interdependent. That is, unlike aconventional polished ferrule, the end face of the fiber can be shapedfor particular application without shaping the mating face of theferrule in a similar fashion. This allows the end face of the fiber tobe shaped to enhance optical performance (for example, angled to reduceback reflection), while the mating face of the ferrule remainsunpolished and essentially normal to the fiber for easy handling andalignment.

This advantage is particularly significant with respect to non-physicalcontacting optical coupling. Specifically, in certain non-physicalcontacting optical coupling applications, such as expanded beamconnectors, which use a ball lens to optically couple connectors, theferrule must be precisely positioned within a ferrule holder such thatthe focal point of the fiber is precisely located relative to theferrule holder. Precisely positioning the focal point is critical toensure that light is effectively coupled to and from the fiber. Thispositioning is typically accomplished by registering a particularsurface of the ferrule on a surface of the ferrule holder. In apreferred embodiment, this registration is accomplished by the leadingedge of the ferrule “seating” on a register surface or shoulder withinthe ferrule holder.

Although this configuration is adequate for multimode applications inwhich the ferrule's mating face is polished normal to the fiber, ittends to be unsuitable for conventional single mode applications inwhich the ferrule's mating face is polished at an angle. Angled polishedferrules are used in single mode applications to reduce back reflectionas mentioned above. Angled polished ferrules, however, areasymmetrical—that is, since they are polished at approximately an 8°angle, their leading edge is actually a point along the periphery of themating face. This asymmetrical aspect of the ferrule makes it difficultfor the ferrule to “seat” precisely on a shoulder in a ferrule holdersince only the point of the ferrule contacts the shoulder. Although theshoulder could be asymmetrical itself to receive the angled ferrule,such a ferrule holder would be difficult to manufacture and costprohibitive. Aggravating the imprecision of seating the point of anangled polished ferrule on the shoulder of the ferrule holder is thefact that the point tends to be sharp, especially in small form factorapplications, and, consequently, tends to either dig into the shoulderor deform As the ferrule digs into the shoulder or deforms, the focalpoint of the fiber relative to the ferrule holder changes, therebyadversely affecting the coupling efficiency of the connector.

In accordance with the present invention, this problem is avoided byproviding a ferrule assembly in which the fiber has an angled end face,but the ferrule has a normal mating face for easy handling andpackaging. For example, referring to FIG. 6, an insert 60 of expandedbeen connector is shown. The insert 60 contains a ferrule 62 which inturn contains a fiber 61. The ferrule 62 is precisely positioned withinthe insert 60 by virtue of a stop 63. More specifically, the stop 63provides a reference surface for the mating face 64 of the ferrule 62 toof expanded been connector is shown. The insert 60 contains a ferrule 62which in turn contains a fiber 61. The fiber 61 comprises an angled endface 66 which is optically coupled with a ball lens 67. The ferrule 62is precisely positioned within the insert 60 by virtue of a stop 63.More specifically, the stop 63 provides a reference surface for themating face 64 of the ferrule 62 to butt up against. Those of skill theart will appreciate that, if the ferrule is precisely positioned withrespect to the insert 60, the focal point of the fiber 61 will also beprecisely positioned relative to the insert. In contrast to aconventional angled polished ferrule, the ferrule 63 shown in FIG. 6 asa mating face 64 normal to the fiber axis. Consequently, the entireperimeter of the mating surface 64 contacts the stop 63 rather than justa single point along the perimeter. This provides for more reliableseating, especially since the entire perimeter of the mating surface isunlikely to dig into the stop 63 (as a point would) and thereby resultin the focal point of fiber 61 moving relative to the insert 60.

In addition to expanded beam connector applications, the preterminatedfiber configuration of the present invention also lends itself to anumber of other non-physical contacting applications in which the focalpoint of the fiber must be controlled precisely by seating the ferruleprecisely. Such applications include, for example, optical couplingswith active devices, such as VCSEL lasers, and passive devices, such asfilters.

It should be apparent from the above description that the ferruleassembly of the present invention provides for significant advantagesover conventional polished ferrule configuration such as lower cost andsimplicity in manufacturing and enhanced versatility with respect to thetype of mating components with which it can effect optically coupling.Still other advantages of the ferrule assembly are anticipated.

1. A process for preparing a ferrule assembly for physical contactoptical coupling, said process comprising: (a) positioning at least onefiber having an end portion in a ferrule having an unpolished matingface such that said end portion extends beyond said unpolished matingface of said ferrule; (b) after step (a), cleaving said end portion ofsaid fiber; (c) after step (b), affixing said fiber relative to saidferrule; (d) after steps (b) and (c), assembling said ferrule assemblyinto an optical package; and (e) optically coupling said ferruleassembly with an optical path of a mating component via physical contactwithout polishing said unpolished mating face and said fiber.
 2. Theprocess of claim 1, wherein step (c) is performed using laser cleaving.3. The process of claim 2, wherein step (b) is performed before step(c).
 4. The process of claim 1, wherein said mating face comprises areflective material.
 5. The process of claim 4, wherein said reflectivesurface comprises copper.
 6. A connector comprising the ferrule assemblyof claim
 1. 7. The connector of claim 6, wherein said connectorestablishes physical contact with a mating connector having a polishedferrule.
 8. The connector of claim 7, wherein said mating connector hasan undercut fiber.
 9. The connector of claim 6, wherein said connectorestablishing physical contact with a mating connector having anunpolished ferrule.
 10. The connector of claim 6, wherein said ferruleassembly is biased forward with a force less than that required todeform said ferrule.
 11. A process for preparing a ferrule assembly forphysical contact optical coupling, said process comprising: (a)positioning at least one fiber having an end portion in a ferrule havingan unpolished mating face such that said end portion extends beyond saidunpolished mating face of said ferrule; (b) after step (a), affixingsaid fiber relative to said ferrule; (c) after step (a), laser cleavingsaid end portion of said fiber using a combination of a laser and aconvergent lens, said combination produces beam having an angle ofconvergence of β from the centerline of said beam and wherein said beamimpinges on said portion at an angle α from the normal plane of saidfiber and at a distance d_(o) from said end face of said ferrule,wherein d_(o) is about 0; (d) after steps (b) and (c), assembling saidferrule assembly into an optical package; and (e) optically couplingsaid ferrule assembly with an optical path of a mating component viaphysical contact without polishing said unpolished mating face and saidfiber.
 12. The process of claim 11, wherein said ferrule has a shapedmating face having angle φ from the normal plane of said fiber, andwherein φα+β.
 13. The process of claim 11, wherein α>β.
 14. The processof claim 11, wherein said beam impinges the fiber at an angle θ from thenormal plane of the fiber and wherein angles θ and α are measuredperpendicular to each other.
 15. The process of claim 14, wherein θ>0.16. The process of claim 14, wherein θ is about
 7. 17. The process ofclaim 14, wherein θ is about
 0. 18. A process for preparing terminatedfibers comprising: (a) positioning at least one fiber in a ferrule suchthat a portion of said fiber extends beyond the mating face of theferrule; (b) after step (a), cleaving said portion of said fiber; (c)after step (b), moving said fiber backward relative to said ferrule suchthat said fiber protrudes from the mating face by a distance d_(f); and(d) after step (c), affixing said fiber relative to said ferrule. 19.The process of claim 18, wherein after (b) said fiber protrudes adistance d_(o) from said end face of said ferrule, wherein d_(o)>0.3 mm.20. The process of claim 18, wherein moving said fiber backward relativeto said ferrule comprises pressing said end face with said fiberprotruding therefrom against a surface to thereby push said fiberbackward relative to said ferrule.
 21. The process of claim 20, whereind_(f)=0.
 22. The process of claim 20, wherein said end face is pushedagainst said surface at an angle such that said mating face is not flushwith said surface, thereby d_(f)>0.
 23. The process of claim 18, whereind_(f)>0.